1. Field of the Invention
The present patent specification relates to a display device and more particularly to a display device including pixels that employs light-emitting elements such as organic electroluminescent (EL) elements.
2. Description of the Related Art
Some organic EL display devices have an optical micro-cavity structure where a distance between a reflecting layer and a semitransparent reflecting layer in pixels is regulated according to wavelength of light emitted from a light emitting layer. In most of the devices, the reflecting layer and the semitransparent reflecting layer are employed as electrodes, and the light emitting layer is formed between the reflecting layer and the semitransparent reflecting layer. The light emitted from the light emitting layer repeatedly reflects on and between the semitransparent reflecting layer and the reflecting layer. Consequently, light having wavelength that matches to the light path length (distance) between the semitransparent reflecting layer and the reflecting layer is intensified to pass through the semitransparent reflecting layer. Such a micro-cavity structure improves color purity of light and luminous efficiency.
Some organic EL display devices include a white pixel in addition to chromatic color pixels such as a red pixel, a green pixel, and a blue pixel. The white pixel contributes to improve the luminance of an image and reduce the power consumption.
As described above, the micro-cavity structure intensifies only light having a particular wavelength that matches to the light path length. Therefore, a white pixel having the micro-cavity structure would not emit pure white light. Accordingly, the micro-cavity structure is not good to the white pixel. In regard to this problem, the display device described in JP2011-165664A includes the micro-cavity structure in the chromatic color pixels and does not include the semitransparent reflecting layer in the white pixel. That is, the micro-cavity structure is not formed in the white pixel. Such display device has both of the advantage obtained from the white pixel and the advantage obtained from the micro-cavity structure formed in the chromatic color pixels.